Apparatus for welding multiply webs of synthetic thermoplastic material

Abstract

An apparatus for welding webs of synthetic thermoplastic material as they move around a deflecting roller comprises an elongate housing, which is movable toward the deflecting roller to assume a position in which said housing is approximately concentric to said roller and closely surrounds said roller around a part of its periphery, and said housing is provided with at least one longitudinally extending hot-air duct, which is curved in the same sense as the housing and is provided with an inlet for receiving flowing hot air and is formed with a plurality of outlet bores or gaps in that wall of the housing which faces the deflecting roller. In order to minimize heat losses, the housing contains a second passage, which approximately concentrically surrounds the hot-air passage and contains an elongate heating element, and the second passage adjacent to one end thereof is provided with an inlet opening for receiving flowing air and adjacent to its opposite end is provided with an opening or line through which the second passage communicates with the hot-air passage.

We claim: 
     
       1. An apparatus for welding webs of synthetic thermoplastic material as they move around a deflecting roller, which apparatus comprises an elongate curved housing, which is movable toward the deflecting roller to assume a position in which said housing is approximately concentric to said roller and closely surrounds said roller around a part of its periphery, and said housing is provided with at least one longitudinally extending hot-air passage, which is curved in the same direction as the housing and is provided with an inlet opening approximately at the center of its length for receiving flowing hot air and is formed with a plurality of outlet bores or gaps in that wall of the housing which faces the deflecting roller, and the housing contains a second curved passage, which approximately concentrically surrounds the hot-air passage and contains an elongate heating element, the second passage adjacent to one end thereof is provided with an inlet port for receiving flowing air and adjacent to its opposite end is provided with an outlet opening through which the second passage communicates with the hot-air passage, and the second passage which contains the heating element, communicates with the hot-air passage through a line connected to said outlet opening and which opens into the hot-air passage through said inlet opening.   
     
     
       2. An apparatus according to claim 1, characterized in that the heating element comprises a heating coil. 
     
     
       3. An apparatus according to claim 1, characterized in that a pair of hot-air passages and a pair of second passages, which contain respective heating elements, are provided in the housing, and the passages of each of said pairs are separated at inner ends thereof by partitions of the housing. 
     
     
       4. An apparatus according to claim 3, characterized in that the respective inlet ports of the seond passages are provided at outer ends of the second passages.